Wine Arcana

Concept

Wine fining

Wine fining is the addition of a material that binds or gathers selected wine components so they can be removed. A winemaker may use it to clarify a hazy wine, reduce astringency or bitterness, or remove proteins that could form a deposit after bottling. The choice of fining agent follows the problem to be solved.

Fining can bring small particles together into larger aggregates and encourage them to settle. The winemaker then separates the wine from the deposit by racking, which means drawing off the clear liquid, or by filtration. Fining and filtration often form successive steps in preparing a wine for bottling.

Matching the agent to the purpose

Bentonite is a fine clay whose negatively charged surfaces bind positively charged proteins in wine. It is widely used to stabilize white wines against protein haze. Egg white and gelatin bind phenolic material and can soften the astringency of red wines. Casein, a milk protein, is used chiefly in white wines to reduce phenolic compounds associated with bitterness and browning.

Another agent, polyvinylpolypyrrolidone, usually called PVPP, binds phenolic compounds and can reduce bitterness and unwanted colour. Its effects increase with dose, so treatment can also remove desirable colour or flavour.

Proteins from peas and potatoes provide plant-derived options for fining. The International Organisation of Vine and Wine describes their use for clarity, stability, and taste, with preliminary trials to select the treatment.1. International Organisation of Vine and Wine, “Fining using proteins of plant origin,” International Code of Oenological Practices, II.3.2.7.

Protein stability

A clear white wine may still contain dissolved grape proteins that later aggregate into haze. Bentonite treatment reduces that potential by removing unstable proteins before bottling. The required dose depends on the wine and must be established by testing.

In a heat-stability test, a laboratory heats a prepared sample, allows it to cool, and compares its turbidity with an unheated control. The heating challenges the proteins' stability, and the cooling period allows aggregates to form. Comparing samples treated with different bentonite doses helps identify an effective addition. Consistent heating and cooling conditions matter because they affect the amount of haze observed.2. Australian Wine Research Institute, “Measurement of heat stability of wine,” sections on heat testing and interpretation.

Choosing the extent of treatment

Small trials let the winemaker compare several doses against untreated wine. Tasting assesses changes in aroma, flavour, and texture, while analysis checks the relevant stability goal. The material and preparation used in the trial should match those used in the cellar.

For a tannic red wine, removing some tannin may make the texture more supple. Further removal may leave the wine less substantial. For a white wine at risk of protein haze, the treatment must remove enough unstable protein to meet the stability goal.

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